Devices for aligning a component are used for a multiplicity of tasks in the prior art. By way of example, drive elements, also called actuators, are used in measurement, control and regulation technology to convert electrical signals into mechanical work. In this regard, it is possible for example for valves to be driven, drive elements to be operated or objects to be lifted. Devices for aligning a component can also be used to stabilize a component or to adjust the alignment thereof. By way of example such a device can be used to take up the weight force of a component and to mount the component.
In projection exposure apparatuses for semiconductor lithography, a multiplicity of actuators, for example plunger coil actuators, are usually used in order to mechanically influence and/or manipulate and/or deform components, in particular optical elements in the illumination system of the projection exposure apparatuses, in order for example to control the beam path of a radiation source.
WO 2005/026801 A2 discloses adjusting optical elements for EUV projection exposure apparatuses, such as mirrors, using driveable movement axes via actuating facilities in the form of Lorentz actuators in a plurality of degrees of freedom. Plunger coil actuators can be used for this purpose, wherein a linearly moveable actuating element, a translator, in the form of a magnet can be moved by electromagnetic interaction with a statically mounted coil surrounding the translator. In this case, the translator is connected via a guide member to the optical element to which a movement carried out is transmitted.
On account of the advancing miniaturization of semiconductor circuits, the desired properties for resolution and accuracy of projection exposure apparatuses are equally increasing. Correspondingly stringent desired properties are also made of the actuator arrangement which mechanically controls the optical elements in the illumination system.
It can be advantageous if the actuators for adjusting the optical elements and the optical elements themselves are decoupled from weight forces as much as possible. Preferably, the actuators adjust the optical elements in the weight-free or apparently force-free state. For this purpose, actuating facilities in the form of so-called weight or gravitation compensation facilities are used which take up the weight forces—at least a large portion of the weight forces—of the optical elements. As a result, the actuation of the optical elements by the actuators is simplified and a lower energy input into the actuators is desired. This in turn has positive effects on the overall behaviour of the projection exposure apparatus, since for example no additional thermal loads on account of the high energy consumption of the actuators are introduced into the installation.
A gravitation compensation facility for optical elements in projection exposure apparatuses is known from DE 10 2009 054 549 A1.
Plunger coil actuators or Lorentz actuators can be used for gravitation compensation. One potential issue here is that the actuators have to be continuously energized, on account of their design, in order to compensate for the static weight force acting on the optical element. The consequence can be a non-negligible evolution of heat, proceeding from the plunger coil actuators to the components, and hence an impairment of the image resolution. A modification of the concept of a plunger coil actuator for weight compensation is known from DE 10 2011 004 607 A1.
A passive weight compensation facility is known from US 2004/0179192 A1. It is proposed to use one or more passive spring elements, for example elastic springs or permanent magnetic fields. However, such spring elements can have the issue of a corresponding mechanical or magnetic stiffness. If the component is intended to be deflected from its neutral position by the actuator, the actuator at least partly compensates for the restoring force acting on the spring, which in turn can results in an undesirable increased energy consumption with resulting production of heat.
Furthermore, a pneumatic weight compensation facility is known from US 2004/0001188 A1. Here a gaseous medium, for example air, is introduced into a pressure chamber, wherein, via a cylinder and a piston, a corresponding force can be exerted on a wafer stage connected to the piston, for the weight force compensation of the wafer stage.
What weight compensation facilities and actuators (in particular linear motors) in the prior art have in common is that an adjustable guide member couples the weight or gravitation compensation facilities and the actuators to the component to be aligned. In this case, the guide member provided for aligning the component can be secured by a head region at a fixing point of the component to be aligned, e.g. an optical element. A foot region of the component can be secured at an actuating element of the actuating facility, e.g. a weight or gravitation compensation facility. Owing to parts tolerances and tolerances in the mounting of individual parts and assemblies, it can happen that one or both mounting or fixing points of the guide member deviate from the setpoint position. Furthermore, it can happen that the actuating facility overall or the component to be aligned and thus also the respectively assigned fixing point are not situated in the setpoint position. By way of example, alignment errors in a range of a few 100 micrometers can occur in projection exposure apparatuses. Such alignment errors can result in considerable differences in the force vector direction in relation to the component, for example a mirror, which can in turn lead to undesired parasitic effects on the mirror and to undesired actuator loads. This can also result in greater evolution of heat.
To reduce mounting errors, particularly in projection exposure apparatuses, a correspondingly great effort is expended during the mounting of the system in order that the components coupled via the adjustable guide member are positioned as optimally as possible with respect to one another. In this case, the movement axis of the guide member should correspond as far as possible to the course of the guide member between its two fixing points. An aggravating additional factor is that, after basic mounting, accessibility to the actuator or to the weight compensation facility is possible only to a limited extent. Moreover, components that are possibly introduced into the installation later can cause further alignment errors which were not able to be taken into account at the time of the basic mounting. A complete compensation of the alignment errors during mounting is therefore not possible or very complex.